Well , I want to suggest more weapons atleast to fill the numbers line on the keyboard.
With a few weapons a game is a game for fun and relaxing , but with many weapons , levels and so , the game becomes more serious about game-play and takes all of your attention. Wont complete it in 2 hours but in 22...and its more interesting , because the 'small' games are fun but only for some time. I hope you understand this because I'm starting to get confused by my own words

(Sorry if something isnt clear in this text,I havent learned English (only from Cartoon Network) so I might say something wrong.)